1. Field of the Invention
The invention relates to a multilayer, sterilizable deep-drawing film, particularly suitable for the manufacturing of vacuum deep-drawn packagings to hold blood infusion fluids, filled in plastic bags, for manufacturing of low temperature resistant vacuum deep-drawing packagings, or for vacuum deep-drawing packaging of sharp-edged packed goods, and a low temperature resistant vacuum deep-drawing packaging with foods packed therein. Such vacuum deep-drawing packaging is manufactured using the deep-drawing film together with a covering film.
2. Description of the Prior Art
Multilayer, sterilizable deep-drawing films are known for the packaging of blood infusion fluids filled into soft PVC bags with a drain valve, as well as for the manufacturing of low temperature resistant packaging. As support films, deep-drawable composite films are used which consist of unextended polyamide or polyester film, laminated with a film of high density polyethylene (HDPE, low pressure polyethylene) or of unoriented polypropylene (PPUG). While such a film can be excellently fused by means of its polyethylene layer, it has the disadvantage that usually two work steps are necessary to manufacture the two film layers and an additional work step is required for joining the film layers Also, there is the disadvantage that in order to achieve a satisfactory deep-drawing behavior, one of the two film layers must be made of polyamide or polyester and functions as a supporting film during the deep-drawing process. Thus, when using these relatively expensive raw materials, one can achieve a satisfactory breaking resistance, but must also accept the fact that the packaging, as a whole, cannot be economically manufactured for the particular end use.
Also, other processes for manufacturing of coextruded composite films became known and the use of these processes makes it possible to manufacture a two-layer or multilayer film in one work step. Essentially, composite films are manufactured according to these processes using tubes provided with two or more annularly arranged nozzles. These processes can be divided into the following three groups:
(a) The tubes are used as such for manufacturing of bag packagings; PA0 (b) The tube films are manufactured in the same manner, however, the tube is cut open and the film is used as a flat film. PA0 (c) Coextruded composite tubes whose individual layers are combined, for instance, by sealing to a uniform composite film so that a separation of the individual layers is no longer possible (German No. OS 19 66 466 and 21 02 377). PA0 (a) a coextruded composite film (1') with two outer layers (A, A') of linear polyethylene, polypropylene, a copolymer of polypropylene, or of high density polyethylene (low pressure polyethylene, HDPE), said outer layers having the same thickness, and two inner layers (B, B'), of an ethylene vinylacetate copolymer, or ethylene methacrylic acid copolymers crosslinked with metal ions, said inner layers having the same thickness; PA0 (b) the outer layers (A, A') being secured to the inner layers (B, B') by melt bonding, and the inner layers (B, B') being secured by heat bonding.
Both cases always result in films with two layers connected with one another, for instance, when using two ring nozzles. Such films and processes are described in German AS No. 11 36 818 and in German patent No. 12 89 297.
Another disadvantage of the known deep-drawing films which occurs particularly in complicated deep-drawing molds, results from the high stiffness of the polyamide or polyester layers. Due to this stiffness, formation of a deep-drawing film having a consistent shape is not always possible.
Another technical disadvantage of the known, sterilizable deep-drawing film is inadequate breaking resistance during evacuation of the bag, connected with a certain embrittlement during heating. This may result in breaking during sterilizing so that reinfection can occur between the outer and inner packaging, i.e., between the support film and the soft PVC bag, whereby the soft PVC bag is no longer sterile.